Character mistake: When Jimmy explains to the kids of the town where the aliens took their parents, he mentions the origin of the aliens being somewhere in the Orion Star System, 3 million light years away. The Orion system is way closer than that. It is actually less than 1400 light years away from Earth. 3 million light years away would place them further than the Andromeda Galaxy.
Suggested correction: This shouldn't be a character mistake. A genius like Jimmy would know something like this. It's basic astronomy.
That's exactly why it's a character mistake. A character mistake is when a character does or says something that they shouldn't based on who/what they are suppose to be, or something a character wrongly states as fact when they should know better.
Character mistake: When Mike pulls out the first Scare Report, the word "yield" is spelled wrong.
Character mistake: When they find a Suicine, they ask Oak and he says it's a Swecon.
Suggested correction: I watched the film, and Professor Oak pronounces Suicune's name correctly.